(1) Field of the Invention
This invention relates to a semiconductor pressure transducer using a measuring diaphragm of semiconductor material for converting a fluid pressure into an electric signal.
(2) Description of the Prior Art
In one type of measuring diaphragm of semiconductor, such as Si, used for sensing pressure known in the art, the measuring diaphragm includes, as described in U.S. Pat. No. 4,303,903, a central portion of small thickness constituting a distortion generating section and an outer peripheral portion of large thickness and has piezo resistor elements located at the distortion generating section to have changes in resistance sensed. In another type of measuring diaphragm of semiconductor, changes in electrostiatic capacity between it and another fixed electrode are measured, as described in U.S. Pat. No. 4,247,274.
Such measuring diaphragm is mounted on a main body by a support member. In view of the ease with which bonding of the measuring diaphragm to the support member can be effected and also by taking into consideration the need to insulate the measuring diaphragm from the main body, it is considered desirable that the support member should be formed of glass (preferably borosilicate glass to obtain agreement in the coefficient of thermal expansion) and the anodic bonding disclosed in U.S. Pat. No. 3,397,278 should be used to effect bonding.
Meanwhile a measuring diaphragm formed of Si and a support member formed of glass are substantially equal to each other in the coefficient of thermal expansion, but they are distinct from each other in Young's modulus of elasticity. The difference in Young's modulus of elasticity should pose no serious problem when the pressure of a fluid to be measured is relatively low. However, when a line pressure (hydrostatic pressure) of over 100 kg/cm.sup.2 is applied, the measuring diaphragm and the support member show a variation in deformation caused by the hydrostatic pressure, so that an output is produced by the hydrostatic pressure and errors tend to occur in the measurements.